I performed the test for about 5 minutes. At 50 frames/sec thats 15000 frames. Thats not enough for you?
Please explain to me why you believe interference is accumulative.
Yes the spark contains frequencies from the fundamental all the way up to light and beyond. But none of it has the code the receiver needs to recognize it.To the receiver all it looks like is garbage. The real wonder of spread spectrum transmission is it can look way down into that garbage and find the transmitted data.
Its like if you dropped your keys in a bucket of mud. You can reach down in that bucket and pull out your keys even though there may be lots of rocks in there. You know they do not have the same feel of the keys.
Please take some time to read up on how spread systems work. You might learn something. I am sure Wiki has an explanation of it